The conventional video game machine has a cross-shaped key which is provided on a controller so that the object displayed on the display is moved by a player's operation of the cross key. Such a cross key is a so-called digital joystick, by which only the direction of movement is designated for the object. With such a cross key, the speed of movement is impossible to designate.
There also is a prior art method where moving speed of the object is varied depending upon the length of the time period over which a cross key is depressed. In such a method, acceleration or deceleration is determined for the object at a constant acceleration rate or a constant deceleration rate by each constant depression time period. Although, in this method, the moving direction and the moving speed of the object can be controlled even by using a digital joystick, there are disadvantages using this approach. That is, the moving speed for the object is merely varied at a constant rate of acceleration or deceleration as determined by software calculations, so that is impossible to arbitrarily control the speed of movement. Furthermore, the speed is determined by the period of key depression time, which requires that the cross key has to be kept depressed for a certain period or longer, resulting in poor responsiveness.
Under such circumstances, the present applicant has proposed by Japanese Provisional Utility Model Publication No. H2-41342, laid open to public on Mar. 22, 1990, a controller which has three contacts arranged in one direction on a cross key thereof so that the moving speed, besides the moving direction, is varied for the object by utilization of changing turning-on of contacts depending upon depression amount of the cross key.
In this prior art, however, the direction of movement is limited to four directions of upper, lower, left and right (and intermediate directions thereof), and the speed of movement is varied only between three stages of speed. That is, in this prior art there still exists limitations on the moving direction and the moving speed.
Although there are already known game machines employing an analog joystick for a control lever of an aircraft, such an analog joystick of the game machines are typically utilized for controlling, for example, the inclination of the aircraft, and wherein control is impossible for the moving direction or the moving speed.